Channel preset device

ABSTRACT

In effecting channel preset, a microcomputer first determines whether or not a broadcasting is on the air on the basis of the presence or absence of a horizontal synchronizing signal obtained through synchronizing separation by a video IC, and if it is thereby determined that the broadcasting is on the air, received broadcasting signal is pulled into a normal tuning point on the basis of an AFC voltage from the video IC, whereupon the corresponding channel is stored if a vertical synchronizing signal from the video IC can be detected at the normal tuning point. Therefore, it is possible to provide a channel preset device which is capable to detecting an on-air channel more reliably and storing the same without adding special circuitry and the like.

BACKGROUND OF THE INVENTION

The present device relates to a channel preset device.

Conventionally, with this type of channel preset device, in a case wherea tuner of a phase-locked loop (PLL) system is adopted, the receivedfrequency of the tuner is sequentially varied with regard to therespective channels on the basis of a predetermined channel plan, and ahorizontal synchronizing signal which is separated from an output of thetuner at each channel frequency is first counted to determine whether abroadcasting is on the air. Here, if it is determined that abroadcasting is on the air, a determination is made as to whether or notthe broadcasting signal can be pulled into a normal tuning point, and ifit is possible, a determination is finally made that the broadcasting ison the air, and that channel is stored as a memory channel. On the otherhand, if the horizontal synchronizing signal cannot be detected, or ifit is impossible even if the horizontal synchronizing signal has beendetected, a determination is made that no broadcasting is on the air,and that channel is stored as a skipped channel.

On the other hand, with a channel preset device disclosed in JapaneseUtility Model Publication No. 5-78073A, a vertical synchronizing signalis separated from a tuner output, noise components included in thevertical synchronizing signal are eliminated, and the verticalsynchronizing signal with the noise components thus eliminated iscounted, thereby determining whether or not a normal tuned state hasbeen obtained.

With the above-described related channel preset devices, the followingproblems have been encountered.

With the former device, there have been cases where even if nobroadcasting is on the air, an erroneous determination can be made thatthe horizontal synchronizing signal has been detected due to the effectof noise or the like. Further, since the AFC pull-in processing iseffected by detecting a point of change in a difference voltagecorresponding to an offset of the frequency of an actual image carrierwave from a reference frequency while varying the received frequency ofthe tuner in finely, there have been cases where a point of change whichoccurs accidentally is detected, and a determination is erroneously madethat a broadcasting is on the air.

On the other hand, with the latter device, since circuitry and the likefor eliminating the noise components which are included in the separatedvertical synchronizing signal are required, the cost has tended tobecome high.

SUMMARY OF THE INVENTION

The present device has been made in view of the above-describedproblems, and its object is to provide a channel preset device which iscapable of detecting an on-air channel more reliably and storing thesame without adding special circuitry and the like.

In order to achieve the above object, there is provided a channel presetdevice comprising:

tuner means for receiving a television broadcasting signal correspondingto a desired frequency and subjecting the television broadcasting signalto predetermined signal processing and outputting the same;

sync separation means for separating horizontal and verticalsynchronizing signals from the output signal of the tuner means andoutputting the same;

on-air judgement means for judging whether a broadcasting is on the airon the basis of the presence or absence of the horizontal synchronizingsignal in the output signal of the sync separation means whilecontinuously varying a received frequency of the tuner means;

tuning-point detection means for detecting a normal tuning point whilevarying the received frequency of the tuner means at neighboringfrequencies of the frequency at which the on-air judgement means judgedthat the broadcasting is on the air; and

channel memory means for storing a channel corresponding to the normaltuning point when it is detected that the vertical synchronizing signalis outputted from the sync separation means at the normal tuning pointdetected by the tuning-point detection means.

In the device, at the time the channel memory means stores an on-airchannel, the on-air judgement means continuously varies the receivedfrequency of the tuner means. Then, the tuner means subjects thetelevision broadcasting signal to predetermined signal processing ateach received frequency and outputs the same, and the sync separationmeans separates horizontal and vertical synchronizing signals from anoutput from the tuner means and outputs the same. The on-air judgementmeans determines an on-air channel on the basis of the presence orabsence of the horizontal synchronizing signal in the output signal ofthe sync separation means. Here, if the on-air judgement means detectsthe on-air channel, the tuning-point detection means detects a normaltuning point on the basis of the output signal of the tuner means whilefinely varying the received frequency of the tuner means. The channelmemory means then stores a corresponding channel if it is detected thatthe vertical synchronizing signal in the output signal of the syncseparation means at the normal tuning point.

Namely, after an on-air channel is first detected on the basis of thepresence or absence of the horizontal synchronizing signal, thebroadcasting signal is pulled into the normal tuning point. Then, adetermination is made again as to whether or not the broadcasting is onthe air on the basis of the presence or absence of the verticalsynchronizing signal at that normal tuning point. If it can bedetermined here that a station is present, the channel is finally storedas the on-air channel. As described above, with the related technique,there have been cases where although no broadcasting is on the air, thetuning point is erroneously detected and a corresponding channel isstored due to the effect of noise or the like. In contrast, inaccordance with the present invention, a determination is made as towhether or not a broadcasting is on the air on the basis of the presenceor absence of the vertical synchronizing signal after detection of thenormal tuning point, so that the on-air channel can be detected morereliably.

Therefore, it is possible to provide a channel preset device which iscapable to detecting an on-air channel more reliably and storing thesame without adding special circuitry and the like.

As the station selection system of the tuner means, it is possible toadopt various systems if they are capable of continuously varying thereceived frequency. For example, in a case where a voltage synthesizersystem is adopted, it suffices if the tuning voltage is supplied to thetuner in such a manner as to cause the received frequency of the tunerto be varied continuously in predetermined frequency units in atelevision broadcast band. It goes without saying that, in such a case,the channel which is stored by the channel memory means is data such astuning voltage value concerning an on-air channel.

Alternatively, there may be configured that: the tuner means includes afrequency synthesizer system for directly controlling a localoscillation frequency of the tuning means in order to tune the system tothe desired frequency in accordance with a predetermined channel plan.

In the device, the on-air judgement means detects an on-air channelwhile continuously varying the received frequency of the tuner means,which has a station selection mechanism of the frequency synthesizersystem, in the channel unit on the basis of a predetermined channelplan. Namely, in the frequency synthesizer system, it is possible totune the system to a desired frequency by directly controlling the localoscillation frequency of the tuner or the like, and the broadcastingsignal is received in each channel unit on the basis of a channel planaccording to a broadcasting form such as normal television broadcastingor cable television broadcasting.

Accordingly, it is possible to provide a specific configuration in thecase where the tuner adopts the frequency synthesizer system.

The tuning-point detection means suffices if it is capable of detectingthe normal tuning point while varying the received frequency of thetuner means in vary small units, and its specific configuration is notparticularly limited.

For example, there may be configured that; the output signal of thetuner means includes information concerning a difference voltage inaccordance with an offset between the received frequency and an imagecarrier wave frequency; and the tuning-point detection means detects thenormal tuning point based on the difference voltage.

In the device, the tuning-point detection means detects the normaltuning point by finely varying the received frequency of the tuner meanswhile monitoring the difference voltage corresponding to an offsetbetween the received frequency and the frequency of the image carrierwave based on the output from the tuner means. That is, the normaltuning point can be detected by utilizing the well-known AFC techniqueor the like.

The significance of detecting the presence or absence of the verticalsynchronizing signal by the channel memory means at the normal tuningpoint detected by the tuning-point detection means lies in reducing thepossibility of erroneously detecting an on-air channel, as describedabove. Here, it goes without saying that a determination may be madeagain as to whether or not a station is present by making use of thecriterion of the presence or absence of the vertical synchronizingsignal, and it does not necessarily mean that a determination is madeagain as to whether or not a station is present solely on the basis ofthe presence or absence of the vertical synchronizing signal.

For example, there may be configured that: the channel memory meansexecutes:

first detection processing for detecting the horizontal synchronizingsignal at the normal tuning point;

second detection processing for detecting the horizontal synchronizingsignal at the normal tuning point, conducted after the lapse of apredetermined time period; and

third detection processing for detecting the vertical synchronizingsignal at the normal tuning point, conducted within the predeterminedtime period.

In the device, when the turning-point detection means detects the normaltuning point, the channel memory means effects first detectionprocessing for detecting the horizontal synchronizing signal from thesync separation means at that normal tuning point. Subsequently, thechannel memory means similarly effects second detection processing fordetecting the horizontal synchronizing signal after the lapse of apredetermined waiting time, and effects third detection processing fordetecting the vertical synchronizing signal from the sync separationmeans during the waiting time. The channel memory means stores thechannel for the normal tuning point if the synchronizing signal can bedetected in each of the synchronous detection processing.

Accordingly, since the on-air channel is determined at the channel onlywhen the synchronizing signal can be detected in each item of thedetection processing. Therefore, it is possible to detect the on-airchannel more reliably and store the same.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic block diagram of a channel preset device inaccordance with an embodiment of the present device;

FIG. 2 is a flowchart illustrating a procedure of channel presetprocessing;

FIG. 3 is a flowchart illustrating the outline of a procedure of on-airjudgement processing;

FIG. 4 is a flowchart illustrating the detail of a procedure of theon-air judgement processing;

FIG. 5 is a voltage waveform diagram illustrating AFC voltagecharacteristic;

FIG. 6 is a diagram illustrating frequency shifts in primary AFCinflection point detection processing; and

FIG. 7 is a diagram illustrating the frequency shift in secondary AFCinflection point detection processing

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, a description will be given of a channel preset deviceaccording to an embodiment of the present invention with reference tothe accompanying drawings.

FIG. 1 is a schematic block diagram of the channel preset device.

In the drawing, a tuner 10 is capable of receiving televisionbroadcasting signals at desired frequencies through a receiving antenna,and selects only a required signal from the received signals, effectshigh-frequency amplification, converts it to an intermediate frequencysignal, and outputs the same. The tuner 10 in this embodiment adopts theso-called PLL system, and the received frequency can be controlled bydirectly controlling the local oscillation frequency on the basis of theinput of predetermined frequency data. It should be noted that thisembodiment is premised on the assumption that the present device isapplied to television broadcasting, but is, of course, applicable toother forms of broadcasting such as cable broadcasting, and theapplication may be altered, as required.

The intermediate frequency signal outputted from the tuner 10 issubjected to video intermediate frequency amplification by a videointermediate frequency (VIF) circuit 20 and is outputted to a video IC30. Meanwhile, an audio intermediate frequency signal is present as afrequency-modulated signal which is 4.5 MHz lower than 58.75 MHz whichis the frequency of the video intermediate frequency signal, and thesignal after being subjected to the intermediate frequencyamplification, if amplitude detected by an unillustrated diode, isextracted as a second audio intermediate frequency signal at 4.5 MHz.The second audio intermediate frequency signal which is extracted hereis subjected to FM detection by an audio IC 40, and is then amplifiedappropriately and is outputted. It goes without saying that, in thisembodiment, the tuner 10 and the VIF circuit 20 as a whole constitutetuner means of the present invention.

The video IC 30, after effecting video detection with respect to theinputted signal, subjects its detection output to various signalprocessing and outputs a video signal, and separates horizontal andvertical synchronizing signals from the detection output and outputs thesame. Accordingly, in this embodiment, the video IC 30 constitutes syncseparation means of the present invention. Further, this video IC 30generates an AFC voltage corresponding to the offset of the frequency ofan actual image carrier wave from the reference frequency, and suppliesthe aforementioned horizontal and vertical synchronizing signals and theAFC voltage to a microcomputer 50.

The microcomputer 50 is capable of supplying frequency data to the tuner10, and the received frequencies of the tuner 10 are controlled by themicrocomputer 50. More specifically, if an operation is effected so asto receive a desired channel by using a remote controller 60, acorresponding infrared remote control signal is transmitted. Themicrocomputer 50 then receives the infrared remote control signalthrough an unillustrated unit for receiving the remote control signal,and sends frequency data to the tuner 10 so as to receive acorresponding channel.

Since actual television broadcasting signals are not necessarily presentat the respective channels, in this embodiment, a so-called channelpreset function is provided whereby on-air channels where televisionbroadcasting signals are present are stored in advance, and stations areselected on the basis of the stored contents. In the channel presetaccording to the present invention, each channel judged as the on-airchannel is stored into an electrically-erasable programmable ROM(EEPROM) 70 as a memory channel, and each channel judged as an off-airchannel is stored into the same as a skipped channel. Next, a detaileddescription will be given of this channel preset function.

In effecting the channel preset, a channel preset instruction is issuedby such as depressing an unillustrated operation button on the remotecontroller 60. Then, an infrared remote control signal is similarlytransmitted from the remote controller 60, and the microcomputer 50detects the signal and executes the channel preset processing inaccordance with a flowchart such as the one shown in FIG. 2. In thedrawing, initial channels are first set in step S110. Namely, initialchannels are set on the basis of a channel plan according to abroadcasting form such as normal television broadcasting, CATV-NORMAL,or CATV-HRC.

Then, a determination is made as to whether a set channel is an on-airchannel or not by executing predetermined on-air judgement processing instep S120, and the fact of the channel being either one of theaforementioned memory channel and the skipped channel is stored in acorresponding channel position of the EEPROM 70 as a result of thedetermination. Subsequently, in step S130, a determination is made as towhether or not the channel is a last channel, and if it is not the lastchannel, in step S140, after setting an ensuing channel on the basis ofthe aforementioned channel plan, similar processing is executed, andupon completion of the processing of the last channel, the channelpreset ends.

FIGS. 3 and 4 show the processing procedure of the aforementioned on-airjudgement processing through flowcharts. In this on-air judgementprocessing, first, in step S205, frequency data (center frequency f0)for receiving the channels which are set as described above is sent tothe tuner 10. Then, the tuner 10 tunes to the frequency corresponding tothe frequency data by directly controlling the local oscillationfrequency. Here, if a television broadcasting signal is present at thatfrequency, the video IC 30 separates horizontal and verticalsynchronizing signals from a video detection output based on the outputof the tuner 10 and supplies them to the microcomputer 50, and suppliesto the microcomputer 50 an AFC voltage corresponding to the offset ofthe frequency of the image carrier wave from the reference frequency.

It goes without saying that if the television broadcasting signal isabsent at the aforementioned frequency, the horizontal synchronizingsignal is not supplied to the microcomputer 50. Accordingly, after thelapse of a waiting time of 20 ms, a determination is made in an ensuingstep S210 as to whether or not the horizontal synchronizing signal issupplied. Specifically, if the horizontal synchronizing signal can bedetected 26 to 36 times during the period of 2 ms, a determination ismade that the horizontal synchronizing signal is present. Then, if itcannot be determined that the horizontal synchronizing signal is presentuntil the lapse of 300 ms in total, in step S215, frequency datacorresponding to a frequency which is 1.31 MHz lower than the centerfrequency f0 is sent to the tuner 10. Namely, in a case where thetelevision broadcast signal is present, the television broadcastingsignal should naturally be present at the center frequency, but sincethere is a possibility of the actual broadcast frequency being offset,the received frequency of the tuner 10 is varied.

After the lapse of the waiting time of 20 ms subsequent to thetransmission of the frequency data in step S215 above, in an ensuingstep S220, a determination is similarly made as to whether or not thehorizontal synchronizing signal is present. Then, if it cannot bedetermined that the horizontal synchronizing signal is present until thelapse of 140 ms in total, in step S225, frequency data corresponding toa frequency which is 2.06 MHz lower than the aforementioned centerfrequency f0 is sent to the tuner 10. Subsequently, in an ensuing stepS230, a determination is similarly made as to whether or not thehorizontal synchronizing signal is present, and if it cannot bedetermined that the horizontal synchronizing signal is present until thelapse of 140 ms in total, in step S235, frequency data corresponding toa frequency which is 1.31 MHz higher than the aforementioned centerfrequency f0 is sent to the tuner 10.

In this case as well, in an ensuing step S240, a determination is madeas to whether or not the horizontal synchronizing signal is presentuntil the lapse of 140 ms in total, and if it cannot be determined thatthe horizontal synchronizing signal is present, in step S245, thefrequency data corresponding to the center frequency f0 is sent again tothe tuner 10. Then, in an ensuing step S250, a determination issimilarly made as to whether or not the horizontal synchronizing signalis present until the lapse of 140 ms in total, and if it cannot bedetermined that the horizontal synchronizing signal is present, in stepS255, the fact of the channel being a skipped channel is stored in thechannel position corresponding to the aforementioned center frequencyf0. Of course, in this embodiment, the microcomputer 50 which executesthe processing in steps S210, S220, S230, S240, and S250 for eachchannel frequency constitutes on-air judgement means.

Meanwhile, if it is determined in steps S210, S220, S230, S240, and S250that the horizontal synchronizing signal is present, predetermined AFCinflection point detection processing is respectively executed in stepsS260, S265, S270, S275, and S280 so as to determine whether or not theAFC inflection point can be detected.

Here, before giving a description of the aforementioned AFC inflectionpoint detection processing, a description will be given of the voltagecharacteristic of the AFC voltage. As shown in FIG. 5, this AFC voltagehas a voltage characteristic which is inversely S-shaped with the normaltuning point F as the center, and in a case where the frequency of anactual image carrier wave coincides with the reference frequency, theAFC voltage becomes a voltage B, and a monotonously increasing ormonotonously decreasing tendency is exhibited in correspondence with thedirection of the offset if the two voltages are slightly offset fromeach other, and the upper side and the lower side of the voltage Bbecome saturated and fixed if the two voltages are greatly offset fromeach other. Accordingly, if the AFC voltage actually supplied from thevideo IC 30 and is compared with the voltage B, the direction of theaforementioned offset becomes clear.

The aforementioned AFC inflection point detection processing consists ofprimary AFC inflection point detection processing and secondary AFCinflection point detection processing. First, in the primary AFCinflection point detection processing, as shown in FIG. 6, the frequencydata is sent in such a manner as to consecutively vary the receivedfrequency of the tuner 10 in units of 82.895 kHz/30 ms in correspondencewith the direction of the actual offset by setting as a starting pointthe frequency f1 at which the horizontal synchronizing signal wasdetected and by setting ±2.44 MHz as an upper limit and a lower limit.Then, if a television broadcasting signal is present, the AFC voltagesupplied from the video IC 30 gradually assumes a value close to thevoltage B, and after crossing over a value which is closest to thevoltage B, the AFC voltage moves away from the voltage B again. Namely,it means that the direction of offset changes after the AFC voltagecrosses over the tuning point at this point of time, and this point isreferred to as the AFC inflection point. Here, in a case where the AFCinflection point cannot be detected even if the frequency isconsecutively varied, and the aforementioned upper limit or lower limithas been reached, a determination is made as to whether or not the AFCvoltage does not change again after waiting for 45 ms for the sake ofreconfirmation. In this case as well, if the AFC voltage does notchange, it is determined that the AFC inflection point is absent.

On the other hand, if the aforementioned AFC inflection point isdetected in the primary AFC inflection point detection processing, thesecondary AFC inflection point detection processing is then started. Inthis secondary AFC inflection point detection processing, as shown inFIG. 7, the frequency data is sent in such a manner as to consecutivelyvary the received frequency of the tuner 10 in units of 27.965 kHz60 msin correspondence with the direction of the actual offset by setting asa starting point the frequency f2 at the point of time when the AFCinflection point was detected in the above-described primary AFCinflection point detection processing and by setting ±9.44 MHz as anupper limit and a lower limit. Then, if a television broadcasting signalis present, the AFC inflection point is similarly detected. However, inthis secondary AFC inflection point detection processing, since thefrequency is varied in smaller steps than in the primary AFC inflectionpoint detection processing, an AFC inflection point which is closer tothe normal tuning point is detected. Further, in a case where the AFCinflection point cannot be detected even if the frequency isconsecutively varied, and when the aforementioned upper limit or lowerlimit has been reached, detection is made as to whether or not the AFCvoltage does not change again after waiting for a duration of 45 ms inthe same way as in the above-described primary AFC inflection pointdetection processing.

The significance of the primary and secondary AFC inflection pointdetection processing is as follows.

Namely, whether or not the television broadcasting signal is present ineach channel frequency can be essentially determined by the presence orabsence of the horizontal synchronizing signal, but due to the effect ofnoise or the like an erroneous determination can be made that abroadcasting is on the air although a broadcasting is actually off theair. Accordingly, even if the horizontal synchronizing signal isdetected, a determination is made as to whether or not the broadcastingsignal can be pulled into the normal tuning point by the primary andsecondary AFC inflection point detection processing More specifically,the AFC inflection point is roughly detected by the primary AFCinflection point detection processing, and the AFC inflection point isdetected more precisely by the secondary AFC inflection point detectionprocessing. Then, if the AFC inflection point cannot be detected by thefirst or secondary AFC inflection point detection processing, it isassumed that the horizontal synchronizing signal has been erroneouslydetected due to the effect of noise or the like, and a determination ismade that the television broadcasting signal is actually absent. It goeswithout saying that, in this embodiment, the microcomputer 50 forexecuting the aforementioned primary and secondary AFC inflection pointdetection processing constitutes tuning-point detection means of thepresent invention.

If the AFC inflection point cannot be detected in steps S260, S265,S270, and S275, it is determined that the television broadcasting signalis absent at each frequency, and the operation respectively proceeds tosteps S215, S225, S235, and S245 to send ensuing frequency data.Further, in steps S220, S230, S240, and S250, the presence or absence ofthe horizontal synchronizing signal is determined in a similar manner.On the other hand, if the AFC inflection point cannot be detected instep S280, it is determined that the television broadcasting signal isabsent at that channel frequency, and in step S255 the fact of thatchannel being a skipped channel is stored in a corresponding channelposition.

On the other hand, if the AFC inflection point can be detected in stepsS260, S265, S270, and S275, in step S310, the presence or absence of thehorizontal synchronizing signal from the video IC 30 is determined atthe received frequency corresponding to that AFC inflection point. Here,if it is determined that the horizontal synchronizing signal is present,the presence or absence of the vertical synchronizing signal from thevideo IC 30 is determined in step S320. More specifically, if thevertical synchronizing signal can be detected at least once until thelapse of 100 ms in total, it is determined that the verticalsynchronizing signal is present. Then, if it is determined that thevertical synchronizing signal is present, in step S330, the presence orabsence of the horizontal synchronizing signal is determined again afterthe lapse of 100 ms in total, and if it is determined here that thehorizontal synchronizing signal is present, in step S340, the fact ofthe channel being a memory channel is stored in the correspondingchannel position. On the other hand, if it is determined in any of stepsS310, S320, and S330 that the synchronizing signal is absent, in stepS350, the fact of the channel being a skipped channel is stored in thecorresponding channel.

As described above, in this embodiment, after the normal tuning point isdetected by the AFC inflection point detection processing, the presenceor absence of the horizontal synchronizing signal is detected at thatnormal tuning point, the presence or absence of the horizontalsynchronizing signal is detected again after the lapse of apredetermined waiting time, the presence or absence of the verticalsynchronizing signal is detected during the waiting time, and if thesynchronizing signal can be detected in each detection processing, thefact of the channel being a memory channel is stored. The microcomputer50 and the EEPROM 70 in executing these items of processing constituteschannel memory means of the present invention. In addition, it goeswithout saying that, by adopting the above-described configuration, itbecomes possible to detect more reliably only on-air channels and storethem.

Next, a description will be given of the operation during channel presetin accordance with the embodiment configured as described above.

If a channel preset instruction is issued by such as depressing anunillustrated operation button on the remote controller 60, apredetermined infrared remote control signal is transmitted from theremote controller 60, and the microcomputer 50 detects the signal andexecutes the channel preset processing. In this channel presetprocessing, initial channels are first set on the basis of a channelplan according to a broadcasting form such as normal televisionbroadcasting, CATV-NORMAL, or CATV-HRC (step S110), and on-air judgementprocessing for determining whether or not a station is present on thechannel (step S120)

In this on-air judgement processing, the microcomputer sends to thetuner 10 the frequency data with respect to the center frequency f0 ofthe aforementioned set channel (step S205). Then, the tuner 10 tunes tothe corresponding frequency on the basis of that frequency data andoutputs an intermediate frequency signal to the VIF circuit 20, which inturn subjects the intermediate frequency signal tointermediate-frequency amplification and then outputs the same to thevideo IC 30. The video IC 30 effects video detection with respect to theamplified video intermediate frequency signal, subjects its detectionoutput to various signal processing to output a video signal, andseparates the horizontal and vertical synchronizing signals from thedetection output and outputs the same. Further, the video IC 30generates an AFC voltage corresponding to the offset of the frequency ofthe actual image carrier wave from the reference frequency, and suppliesthe horizontal and vertical synchronizing signals and the AFC voltage tothe microcomputer 50.

The microcomputer 50 determines the presence or absence of thehorizontal synchronizing signal from the video IC 30, and if it cannotbe determined that the horizontal synchronizing signal is present, thereceived frequency of the tuner 10 is varied in the range between(f0−2.06) MHz and (f0+1.31) MHz until it can be determined that thehorizontal synchronizing signal is present (steps S210 to S250). Ofcourse, in a case where the television broadcasting signal is absent,the horizontal synchronizing signal is absent even if the receivedfrequency is varied. Accordingly, as a result of varying the receivedfrequency of the tuner 10, if it cannot be determined that thehorizontal synchronizing signal is present, the fact of the channelbeing a skipped channel is stored in the corresponding channel positionof the EEPROM 70 (step S255).

On the other hand, if it is determined that the horizontal synchronizingsignal is present, predetermined AFC inflection point detectionprocessing is executed by using the received frequency of the tuner 10as a starting point (steps S260, S265, S270, S275, and S280). Namely, ifthe received frequency of the tuner 10 is offset from the normal tuningpoint on the basis of the AFC voltage supplied from the video IC 30, thefrequency is varried in very small steps in correspondence with thedirection of the actual offset, and the AFC inflection point at whichthe direction of the offset changes is detected. Of course, to detectthe AFC inflection point is none other than to detect the normal tuningpoint, and even in a case where it is determined that the horizontalsynchronizing signal is present, if the AFC inflection point cannot bedetected, it is determined that the television broadcasting signal isabsent. In addition, even if the horizontal synchronizing signal isdetected in the frequency band ranging between (f0−2.06) MHz and(f0+1.31) MHz, if the AFC inflection point cannot be detected, the factof the channel being a skipped channel is stored in the correspondingchannel position (step S255).

On the other hand, if the AFC inflection point can be detected, thepresence or absence of the horizontal synchronizing signal from thevideo IC 30 is detected at the received frequency at which the AFTinflection point was detected (step S310). Here, if the presence of thehorizontal synchronizing signal has been detected, the presence orabsence of the vertical synchronizing signal from the video IC 30 isdetected until the lapse of 100 ms in total (step S320). Then, if thepresence of the vertical synchronizing signal has been detected, thepresence or absence of the horizontal synchronizing signal is detectedagain after the lapse of 100 ms in total (step S330). Thus, if thepresence of the synchronizing signals has been detected in all thedetection processes, the fact of the channel being a memory channel isstored in the corresponding channel position (step S340). Meanwhile, ifthe absence of the synchronizing signal has been detected in any one ofthe detection processes, the fact of the channel being a skipped channelis stored in the corresponding channel position (step S350).

Thereafter, by similarly executing the on-air judgement processing whilesetting the channels consecutively on the basis of a predeterminedchannel plan, the fact of the channel being either a memory channel or askipped channel is stored in the corresponding channel position, andupon completion of the processing of the last channel, the channelpreset ends (step S120-S140).

As described above, the arrangement provided is such that, in effectingthe channel preset, the microcomputer 50 first determines whether or nota broadcasting is on the air on the basis of the presence or absence ofthe horizontal synchronizing signal obtained through synchronizingseparation by the video IC 30, and if it is thereby determined that thebroadcasting is on the air, the broadcasting signal is pulled into thenormal tuning point on the basis of the AFC voltage from the video IC30, whereupon the corresponding channel is stored if the verticalsynchronizing signal from the video IC 30 can be detected at the normaltuning point Therefore, it is possible to provide a channel presetdevice which is capable to detecting an on-air channel more reliably andstoring the same without adding special circuitry and the like.

What is claimed is:
 1. A channel preset device comprising: tuner meansfor receiving a television broadcasting signal corresponding to adesired frequency and subjecting the television broadcasting signal topredetermined signal processing and outputting the same: sync separationmeans for separating horizontal and vertical synchronizing signals fromthe output signal of the tuner means and outputting the same; on-airjudgment means for provisionally judging whether a broadcasting is onthe air on the basis of the presence or absence of the horizontalsynchronizing signal in the output signal of the sync separation meanswhile continuously varying a received frequency of the tuner means;tuning-point detection means for detecting a normal tuning point whilevarying the received frequency of the tuner means at neighboringfrequencies of the frequency at which the horizontal synchronizingsignal is detected, so that whether the broadcasting is on the air isjudged; and channel memory means for storing a channel corresponding tothe normal tuning point when it is detected that the verticalsynchronizing signal is outputted from the sync separation means at thenormal tuning point detected by the tuning-point detection means.
 2. Thechannel preset device as set forth in claim 1, wherein the tuner meansincludes a frequency synthesizer system for directly controlling a localoscillation frequency of the tuning means in order to tune the system tothe desired frequency in accordance with a predetermined channel plan.3. The channel preset device as set forth in claim 1, wherein the outputsignal of the tuner means includes information concerning a differencevoltage in accordance with an offset between the received frequency andan image carrier wave frequency, and wherein the tuning-point detectionmeans detects the normal tuning point based on the difference voltage.4. The channel preset device as set forth in claim 1, wherein thechannel memory means confirms that the horizontal synchronizing signalis detected at the normal tuning point, before and after the detectionof the vertical synchronizing signal.
 5. The channel preset device asset forth in claim 3, wherein the tuning-point detection means detectsthe normal tuning point while varying the received frequency roughly atfirst, and subsequently varying finely.
 6. A channel preset methodcomprising the steps of: receiving a television broadcasting signalcorresponding to a desired received frequency; separating horizontal andvertical synchronizing signals from the received broadcasting signal;judging provisionally whether a broadcasting is on the air on the basisof the presence or absence of the horizontal synchronizing signal in thebroadcasting signal while continuously varying the received frequency;detecting a normal tuning point while varying the received frequency atneighboring frequencies of the frequency at which the horizontalsynchronizing signal is detected, so that whether the broadcasting is onthe air is judged; detecting the vertical synchronizing signal at thenormal tuning point; and storing a channel corresponding to the normaltuning point when the vertical synchronizing signal is detected in thebroadcasting signal at the normal tuning point detected by thetuning-point detection means.
 7. The channel preset method as set forthin claim 6, wherein the normal tuning point is detected based oninformation concerning an offset between the received frequency and animage carrier wave frequency.
 8. The channel preset method as set forthin claim 6, further comprising the steps of: detecting the horizontalsynchronizing signal at the normal tuning point, before and after thestep of detecting the vertical synchronizing signal to store thechannel.
 9. The channel preset method as set forth in claim 7, whereinthe normal tuning point is detected while varying the received frequencyroughly at first, and subsequently varying finely.